Effects of radiation on murine T-cell leukemogenesis induced by butylnitrosourea

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Abstract
BDF1 mice were exposed to butylnitrosourea for 12 weeks (BNU, 0.02% in the drinking water) and died of thymic lymphomas with median latency periods of 12–20 weeks. In addition to BNU, groups of mice received weekly radiation doses of 0.0625–1.0 Gy; 12×0.25 Gy enhanced leukemogenesis, 12×0.75 Gy delayed it and 12×0.50 Gy had no effect. Lower doses had marginal enhancing effects. After a dose of 12×1.0 Gy, the mice died earlier than after treatment with BNU alone and, as with 12×0.75 Gy, some extrathymic lymphomas were observed. The numbers of CFU-S in the femur and the spleen showed a dose-dependent depression, in addition to the effect of BNU alone. In lymphocyte stimulation assays with Con A und LPS and also in the mixed lymphocyte reaction, a reduced proliferation was found, again dependent on the radiation dose. Therefore, there was no correlation of leukemogenesis and the degree of stem-cell reduction or depression of these immune parameters. The delay of leukemogenesis by 12×0.75 Gy in addition to BNU may be caused by an enhanced target cell kill.